Piston rings are well known. They are usually received within an annular groove disposed about an outer periphery of a piston. The piston reciprocates within a cylinder chamber of an internal combustion engine, compressing fluids such as gases within the cylinder into a combustion chamber. These fluids are ignited and expand within the combustion chamber, forcing the piston away from the point of ignition.
The primary function of piston rings is to provide an effective seal of the gases, called "blow-by control", and is accomplished by placing a first piston ring, called a compression seal, near the uppermost portion of the piston. The compression seal is designed to seal during an up-stroke of the piston to compress the gases within the chamber. A secondary function of piston rings is to prevent excess lubricating oil from entering the combustion chamber. To accomplish the secondary function, a second piston ring, called an oil seal, is placed below the compression seal to prevent oil from being carried up into the combustion chamber. Thus, the compression seal and the oil seal both cooperate to seal the combustion chamber from escaping gases or entering lubricating oil.
Generally, a piston reciprocating in a cylinder chamber creates a great deal of friction between the outer surface of the piston and the adjacent cylinder wall. Oil is used to lubricate the contacting surface between the piston and the cylinder wall. The oil used to lubricate tends to move up the cylinder wall from the oil sump, providing a smooth lubrication surface across which the piston may traverse. Commonly, excess oil from the oil sump migrates through the piston chamber and is allowed to move up the cylinder wall unrestrained. Inevitably, some oil passes the piston rings or seals designed to retard oil movement into the combustion chamber. Typically, the piston rings or seals wear through use causing the seals to fail and permitting unwanted oil to enter the combustion chamber. Additionally, piston rings also may not provide proper seals to contain oil because the rings tend not to effectively contact the cylinder wall due to pressure from blow-by gases that are created by explosions in the combustion chamber and the hydrodynamic influence of the oil on the cylinder wall. Blow-by gases tend to move out of the combustion chamber and down the cylinder wall. The pressure produced by the blow-by gases pushes the compression rings away from the cylinder wall. Consequently, oil on the cylinder walls may pass the rings and again enters the combustion chamber.
Once in the combustion chamber, the oil ignites. The burning of oil in the combustion chamber not only wastes oil, but it causes the internal combustion engine to emit unwanted excess noxious gases. Consequently, additional catalyst is required in the catalytic converter to treat the excess noxious gases prior to exhausting the gases into the environment.
To overcome these problems, pistons have been designed to encompass oil rings with openings used to drain oil. However, holes used to drain oil are typically susceptible to a problem called reverse oil pumping where oil flows from the interior of the piston through blow-by relief openings to the cylinder wall. This event may actually allow more oil to ultimately enter the combustion chamber. Accordingly, the problem of unwanted oil entering the combustion chamber from the piston chamber remains.